Radiolabelled nanoparticles are useful tools for biodistribution or cellular uptake studies related to the risk assessment of nanomaterials. Such studies are ideally carried out with industrially manufactured nanoparticles. Irradiation of small quantities of such nanoparticles, in the form of dry powders, with neutrons or light ions allows radiolabelling while preserving their relevant properties. However dry and loosely packed nanoparticle powders exhibit poor thermal conductivity and may overheat under irradiation.
Their effective thermal conductivity is not known and conventional temperature measurement methods are difficult to apply. Reasonably accurate temperature data could be derived from post-irradiation X-ray diffraction studies on anatase TiO2-nanoparticles subjected to proton beams of different intensities. The anatase-to-rutile phase transition starting at about 750◦C was identified by observing rutile peaks in X-ray diffraction patterns. The onset of growth of single diffracting TiO2-domains at around 200◦C was revealed by shape analysis of the diffraction peaks. Identifying these reference temperatures allowed to determine the effective thermal conductivity of the
TiO2-nanoparticle powder target and to calibrate the calculated temperature profile.
The effective thermal conductivity in the TiO2-NP powder target is close to that of the air trapped in the powder. Thus, the contribution of the nanoparticles to the heat removal from the target is negligible and the obtained temperature profile may be considered
as a good estimate for all types of loosely packed nanoparticle powders under light ion irradiation.